This invention relates in general to imaging, and more specifically, to a migration imaging system.
There has been recently developed a migration imaging system capable of producing high quality images of high density, continuous tone, and high resolution. This system is described in the above mentioned application Ser. No. 403,002. In a typical embodiment of this imaging system, an imaging structure comprising a conducting substrate coated with a layer of softenable or soluble material, overcoated with a layer of photosensitive particles is imaged in the following manner: An electrostatic latent image is formed on the photosensitive surface; e.g., by uniform electrostatic charging and exposure to a pattern of activating electromagnetic radiation. The image is then developed by exposing the plate to a solvent which dissolves only the soluble layer. The photosensitive particles which have been exposed to radiation migrate through the softenable layer as it is softened and dissolved, leaving an image on the conductive substrate conforming to a negative of the original. This is known as a positive-to-negative image. Through the use of various techniques, either positive-to-positive or positive-to-negative images may be made depending on the materials used and the charging polarities. Those portions of the photoconductive layer which do not migrate to the conductive substrate may be washed away by the solvent with the softenable layer, or where other developing techniques are used, the softenable layer may at least partially remain behind on the substrate.
In general, three basic imaging members may be used: a layered configuration which comprises a substrate coated with a layer of softenable material, and a fracturable and preferably particulate layer of photosensitive material on or embedded at or near the upper surface of the softenable layer; a binder structure in which the photosensitive particles are dispersed in the softenable layer which overcoats a substrate; and an overcoated structure in which a substrate is overcoated with a layer of softenable material followed by an overlayering of photosensitive particles and a second overcoating of softenable material which sandwiches the photosensitive particles.
In another recently developed imaging system, as disclosed in copending application Ser. No. 520,423, filed Jan. 13, 1966, now abandoned, an image is formed by the selective disruption of a layer of particulate material overlaying an electrostatically deformable film or layer. The imaging structure used in this system is substantially the same as that used in the imaging system already described above, and involves exposing the charged member to an optical image to selectively relocate the charge and form a developable charge pattern. The softenable layer is then developed or softened by heat whereupon the particulate layer is selectively disrupted, resulting in a rearrangement of the particles to form an image viewable by reflected or transmitted light. When the structure is developed by heat, the photosensitive area or layer is disrupted and the photosensitive particles are thereby selectively rearranged to change the optical properties of the plate. The image is believed to be formed because the particles drift on top of one another and accumulate in valleys or pockets of the deformation image leaving the raised portions of the image uncovered. This imaging system is believed to be substantially due to a surface disruption effect with no substantial migration of the photosensitive particles within the softenable layer. This final image differs from that described above, in that the softenable layer is deformed in conjunction with a disruption of the photosensitive particles.
Another related imaging system is directed to the formation of a migration image, and comprises exposing an imaging member to a vapor or heat to form a migration image composed of photosensitive particles, followed by heating said structure, whereby a high density image having low background is produced. This system is described and claimed in copending application Ser. No. 612,122, filed on Jan. 27, 1967, now abandoned. If desired, the migration image formed above may be utilized as a separate image without resorting to the heating step.
These imaging processes usually comprise a combination of process steps which include charging, exposing, and developing with a solvent, its vapor, or heat. The characteristics of these images are dependent on such process parameters as potential, exposure, and development time, as well as the particular combination of the process steps. High density, continuous tone and high resolution are some of the photographic characteristics possible. The image is characterized as a fixed or unfixed photoconductive powder image which can be used in a number of applications such as microfilm, hard copy, optical masks, and stripout applications, using adhesive materials. Alternative embodiments of this concept are further described in the above cited copending applications.
In a related imaging system described in copending application Ser. No. 483,675, filed Aug. 30, 1965, now U.S. Pat. No. 3,656,990, nonphotoconductive particulate material is used to form images in the mode already defined above. In this system, a developable image is formed by charging in image configuration through the use of a mask or stencil. This image is then developed in a solvent for the softenable material. Alternative embodiments of this concept are further described in the above cited copending applications.
Although the above mentioned layered configuration presently used in migration imaging produces images having high quality, it is desirable that other structures be employed which would enable a wider variety of photosensitive materials to be easily employed in the system. With the present layered configuration, certain photoconductors such as selenium, are more advantageously used in a layered configuration, while other inorganic materials, such as, for example, zinc oxide and organic materials such as phthalocyanine may be more advantageously used in configurations other than a layered structure. It is noted that in the above mentioned layered configuration, close tolerances in the particle size of the photosensitive particles are typically maintained to achieve optimum images. A particle size thickness of about 1 or 2 microns or less is usually preferred.
In a new area of technology such as migration imaging, new methods, apparatus, and structures are often discovered for the performance of the novel system in a new mode. The present invention relates to new and advantageous embodiments of migration imaging systems.